How do you perform an arterial blood gas (ABG)?

How to Perform an Arterial Blood Gas (ABG)

The proper technique for performing an arterial blood gas requires assessment with Allen's test first to ensure dual blood supply to the hand from both radial and ulnar arteries, followed by obtaining informed consent, using local anesthesia, and proper sampling technique. 1, 2, 3

Preparation

• Always perform an Allen's test before radial artery puncture to confirm collateral circulation to the hand 1, 3
• Obtain informed consent from the patient, explaining the procedure and possible risks 1, 3
• Use local anesthesia for all ABG specimens except in true emergencies 2, 3
• Gather necessary equipment: pre-heparinized syringe, antiseptic solution, sterile gloves, local anesthetic, gauze, and ice (if analysis will be delayed) 4

Procedure Steps

• Position the patient's wrist extended (for radial artery) with the hand supported on a firm surface 4
• Identify the pulse of the selected artery (radial artery is most commonly used) 3, 4
• Clean the site with antiseptic solution and allow to dry 4
• Administer local anesthetic subcutaneously at the puncture site 2, 3
• Hold the syringe at a 30-45 degree angle (for radial artery) with the bevel facing upward 4
• Insert the needle slowly until arterial blood pulsates into the syringe 4
• Allow the syringe to fill passively with arterial blood (approximately 2-3 mL) 5
• After obtaining the sample, withdraw the needle and apply firm pressure to the site for at least 5 minutes 3, 4
• Expel any air bubbles from the syringe, cap it, and place on ice if analysis will be delayed more than 10 minutes 4

Post-Procedure Care

• Maintain pressure on the puncture site for at least 5 minutes, or longer for patients on anticoagulants 3, 4
• Check the puncture site for bleeding or hematoma formation 4
• Label the sample with patient information and time of collection 4
• Transport the sample to the laboratory immediately or place on ice if analysis will be delayed 5, 4

Common Pitfalls and Considerations

• Failing to perform Allen's test may risk hand ischemia if the radial artery is the sole blood supply 1, 3
• Inadequate local anesthesia can cause unnecessary pain and patient movement during the procedure 2, 3
• Air bubbles in the sample can affect PO2 and PCO2 measurements 5, 6
• Delayed analysis without proper cooling can lead to inaccurate results due to ongoing cellular metabolism 5
• In patients with coagulopathy or on anticoagulants, extended pressure may be needed to prevent hematoma 3

Alternative Approaches

• For patients requiring frequent ABG sampling, consider an indwelling arterial catheter 7
• In non-critical patients, arterialized earlobe blood gases may be used as an alternative to obtain accurate pH and PCO2 measurements, though PO2 is less accurate 2, 3
• Central venous blood gas can be considered in stable patients when arterial access is difficult, with the understanding that arterial pH ≈ venous pH + 0.05 and arterial PCO2 ≈ venous PCO2 - 5 mmHg 7

Indications for ABG Testing

• Critical illness including major trauma, sepsis, shock, and anaphylaxis 2, 3
• Unexpected or inappropriate fall in oxygen saturation below 94% 2, 3
• Deteriorating clinical status in patients with respiratory conditions 2, 3
• Monitoring patients with COPD or other conditions at risk for CO2 retention when starting oxygen therapy 1, 2
• Assessment of acid-base status in patients with suspected metabolic disturbances 2, 3, 6